Bristles having varying stiffness

ABSTRACT

Bristle stiffness is varied by allowing a support beam that carries the bristles to undergo torsional movement in response to brushing action. Torsional movement is achieved by allowing the support beam to be disconnected to the brush head along at least portions of the length of the support beam. In particularly preferred embodiments, brushes employing the varying stiffness techniques are made with bristle sub-assemblies that have at least one row of bristles connected to a base string or similar structure that functions as a support beam. The base string can be connected across an opening in the brush, and is thus connected at its opposite ends, or it can be connected at any number of spaced intervals, the number and length of spacing being selected to achieve a desired degree of stiffness.

[0001] This application is a division of U.S. application Ser. No.09/575,817, filed May 22, 2000, which is a continuation-in-part of U.S.application Ser. No. 09/455,308, filed Dec. 6, 1999 which issued as U.S.Pat. No. 6,351,868, on Mar. 5, 2002 and U.S. application Ser. No.09/092,092, filed Jun. 5, 1998 which issued as U.S. Pat. No. 6,096,151,on Aug. 1, 2000.

RELATED APPLICATIONS

[0002] This case is related to co-pending application Ser. No.09/092,094, by Mark S. Edwards, et al., entitled “Monofilament BristleAssemblies And Methods Of Making Brushes Using Same,” filed Jun. 5,1998; and co-pending application Ser. No. 09/550,657, by Mark S.Edwards, et al., entitled “Method and Apparatus For Making BristleSubassemblies, filed Apr. 17, 2000 (which was based on ProvisionalApplication No. 60/130,883, filed Apr. 23, 1999.

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to brushes and the art ofbrush making, and more specifically, to a bristle sub-assembly in whichbristles are connected at a base end to a supporting “beam,” which couldtake the form of a base string, a bond line, or other structure whichjoins the common base ends of the bristles together in a row. Aparticularly useful application of such bristle sub-assemblies is inbrush structures where segments of bristle sub-assemblies span openareas of a brush head or other supporting structures, and theflexibility of such bristles is at least in part determined by torsionalcharacteristics of the beam.

DESCRIPTION OF THE RELATED ART

[0004] The aforementioned co-pending applications describe a method ofmaking bristle sub-assemblies which involve wrapping a polymericmonofilament around a mandrel and bonding the individual wraps to one ormore base strings by applying thermal energy. According to theaforementioned applications, an apparatus for making bristlesub-assemblies includes a rectangular-shaped mandrel around which iswrapped at least one continuous strand or monofilament. The strands ormonofilaments form a plurality of “wraps” which are then placed incontact with at least one “base string,” which runs generallyorthogonally to the wraps. At the points of contact between the wrapsand the base strings, ultrasonic energy is applied to cause theindividual wraps and base strings to bond together. At a downstreamprocessing point, cutters are used to turn the bonded base strings andwraps into bristle subassemblies.

[0005] One particularly preferred apparatus for making bristlesub-assemblies is shown in FIG. 1, wherein the apparatus 10 includes arectangularly shaped mandrel 12, around which is wrapped a monofilament14. A wrapping mechanism 16 rotates around the mandrel 12, laying out aplurality of “wraps” 18, which are moved vertically along the mandrel 12by a conveyer mechanism, generally referred to by the numeral 20.

[0006] Four base strings 22 are fed into contact with the wraps fromsupply sources (not shown) near respective heating elements 24. Whenenergy is supplied to the ultrasonic heating elements in contact withthe base string, the surfaces of the monofilament wraps and/or the basestrings, which are in contact with each other, become plastic; aftercooling, which occurs immediately after the wraps move away from theheating elements, the wraps of monofilament and the base strings becomebonded together.

[0007] As the bonded wraps and base strings move further away from theheating elements, they pass through cutters 26, only two of four beingseen from the view of FIG. 1. The cutters 26 slit the bonded wraps intofour bristle strings 28, each of which can be taken up on reels (notshown) or other means for further processing.

[0008]FIG. 2 is an enlarged view showing the point of contact of one ofthe monofilament wraps 18 and one of the base strings 22. The basestring is held by a horn 30 of the ultrasonic heating element, while acable 32 of the conveyor mechanism 20 translates the monofilament wrapsup the mandrel 12. The cable 32 and base string move in the samedirection at the same speed, so that the bonded wraps and base stringare moved to the cutters 26 and spit into separate bristle strings 28.

[0009] One of the bristle strings 28 is shown in FIG. 3, as having abase string 22, and two rows 34 and 36 of bristles which are made of themonofilament that had previously been used to form the wraps. Thebristle rows have a tendency to form a V-shape, with the base string atthe vertex of the “V.” Further processing steps can be used to renderthe rows of bristles parallel to each other; alternative orientationscan also be made when desired.

[0010] The details of how the bristle strings are formed, and how theycan be combined with brush bodies to form a variety of brushes, aredescribed in the aforementioned co-pending and related applications,which are incorporated herein by reference. In making brushes using thebristle strings described herein and in the related and co-pendingapplications, the bristle strings are cut into lengths that can becalled “bristle sub-assemblies.” These lengths can be embedded in orotherwise attached to the brush bodies to form a wide variety of sizes,shapes and types of brushes.

[0011] While the bristle sub-assemblies described above have manyadvantages, a continuing need exists for improved brushes and bristlesemployed in same, as well as for methods and means for varying orotherwise controlling the stiffness of the bristles without necessarilychanging the physical parameters of the bristles themselves.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a bristlesub-assembly in which the stiffness of the bristles can be varied bychanging one or more parameters of the beam structure that supports thebristles.

[0013] Another object of the invention is to provide a method of varyingthe stiffness of the bristles of a brush by changing one or moreparameters of the beam structure used to support the bristles of thebrush.

[0014] Still another object of the present invention is to provide amethod of changing the stiffness of a bristle without changing thematerial or diameter of the bristles themselves.

[0015] These and other objects are met by providing a brush whichincludes a brush body, at least one bristle sub-assembly having asupport beam having first and second opposite ends and a row of bristleshaving proximal and distal ends, at least one point of attachmentbetween the brush body and the support beam, thereby defining at least aportion of the bristle sub-assembly that extends into free space, andmeans for varying the stiffness of the bristles of the bristlesub-assembly.

[0016] Preferably the means for varying the stiffness of the bristles isa physical parameter of the beam, such as cross-sectional shape,material properties Young's Modulus, and thickness. Additional means forvarying the stiffness include coating at least a lower portion of thebristles with a polymeric, preferably elastomeric,-material, andaltering the cross-section of the bristles, such as by tapering the endportions.

[0017] These and other objects and features of the invention will bebetter understood in referencing the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic view of an apparatus for forming bristlestrings;

[0019]FIG. 2 is an enlarged, cross-sectional view showing the point ofcontact between a monofilament wrap and a base string, in the apparatusof FIG. 1, and approximately at the ultrasonic heating station;

[0020]FIG. 3 is an elevational view of a bristle string which includesfirst and second rows of bristles connected to a base string;

[0021]FIG. 4 is a vertical, longitudinal sectional view, showing abristle sub-assembly spanning between two points on a brush head acrossan opening or open space;

[0022]FIG. 5 is a vertical, transverse sectional view, taken along lineIV-IV of FIG. 4;

[0023]FIG. 6 is an end view of a bristle sub-assembly in which thelower, or proximal, end portions of the bristles are coated with anelastomeric material to provide additional stiffness;

[0024]FIG. 7 is a chart showing modeling of base string deflection ratioas a function of thickness, or diameter, of the base string;

[0025]FIG. 8 is a side elevational view of a bristle sub-assemblyconnected at spaced intervals to the upper surface of a brush body;

[0026]FIG. 9 is a side elevational view of a bristle sub-assembly, madeaccording to the methods and apparatuses described in the aforementionedco-pending applications;

[0027]FIG. 10 is an end view of the bristle sub-assembly of FIG. 9;

[0028]FIG. 11 is a side elevational view of the bristle sub-assembly ofFIG. 9, after tapering the distal end portions of the bristles, and

[0029]FIG. 12 is an end view of the bristle sub-assembly of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Referring to FIGS. 4 and 5, a bristle sub-assembly 38 has a basestring 40 and two rows 42 and 44 of bristles. The bristle sub-assembly38 is anchored to two fixed structures 46 and 48, between which is anopen space 50. The fixed structures 46 and 48 can be different parts ofthe same brush head, for example, where the head defines an opening andthe bristle sub-assembly 38 spans the opening. For purposes of thepresent invention, the bristle sub-assembly 38 has any length which isunbounded, or freely spanning between opposite ends that are connectedor fixed to a relatively non-movable structure, or semi-rigid structure.

[0031] In the past, stiffness of bristles have been controlled to someextent by varying certain parameters of the bristles, such as theirlength or height, cross-sectional shape, thickness, and the type ofmaterial used. The use of the bristle sub-assemblies made according tothe aforementioned co-pending applications has led to the creation ofrelatively high aspect ratio bristle arrays, meaning long, thin rows ofbristles. These bristle sub-assemblies have the added advantage of beingcost effective to produce.

[0032] One aspect of the present invention is the realization that, ifan individual bristle sub-assembly is suspended in free space, byattachment at its opposite ends to different points on a brush body,another mechanism for controlling stiffness arises: torsional movementand flexion of the base structure of the bristle sub-assembly thatimparts changes in the apparent stiffness of the bristles. In otherwords, the bristles will rotate about the axis of the base string, orother supporting “beam” structure, to thereby feel softer to the touch.Thus, thicker diameter bristles, for example, can be made to feelsofter—or as soft as a thinner bristle monofilament—by changing theproperties of the base string. Those properties include Young's modulusof the material from which the base string or other beam material ismade; the diameter of the base string; the geometry or cross-sectionalshape of the base string; the length of the base string extendingbetween the two attachment points; and the tension imparted in the basestring.

[0033] Additional bristle action or movement can be achieved whensegments of the base of a bristle sub-assembly are allowed to spanbetween attached points. The length of the span can be determined by thetype of brush envisioned, such as a toothbrush as opposed to a vacuumbrush, the overall size, and the degree of movement desired. For a givenmaterial, base string geometry and diameter, bristle diameter andbristle height, all held constant within a bristle sub-assembly, thesoftness of the bristles will vary according to position along thenon-attached segment of the bristle sub-assembly, with the first andlast bristles having the highest stiffness and the center bristles beingthe most soft.

[0034] The continuous change in sensible stiffness for a constant forceapplied along the suspended length is produced by the differentialdisplacement of each bristle tip according to the cumulativecontributions generated from the bending of the bristle, the degree ofrotation of the base string (torsional motion) at the base of thebristle, the bending or flexion of the base string at the bristle base,and the selection of material properties for the base string. Bristleswithin a bristle sub-assembly, located at or juxtaposed the anchoringpoint to the brush head have limited motion, primarily bending motionand are similar to bristles tufted into a tuft hole of a conventionalbrush. While the bristles located near the anchor point exhibit movementsimilar to that of a conventional brush, bristles more distant to theanchor point exhibit an increasingly lower stiffness value (highermovement) due to the contribution of the base string component.

[0035] The base string described above can be a separate strand ofmaterial, as in the preferred embodiments of the prior cop-endingapplications, or other “beams” can be formed by the fused area ofbristles not connected to a base string, such as when bristles are laidside by side and fused together at the base. The fused area becomes thebeam or base string. A glue line or extrusion line could also be used toform the beam.

[0036] By mixing and matching the parameters described above, one canachieve virtually any desired degree of bristle stiffness. The bristlesub-assembly product can be customized to a stiffness range by combiningphysical dimensions, and whether they are solid or have voids. The spandistance between anchor points and to some degree the tension will alsocontribute to customizing the range of movement.

[0037] The bristles in a linear bristle sub-assembly, such as thosedescribed in the co-pending applications, are freer to move thanbristles densely packed in a conventional tuft hole. Conventionaltufting techniques pack tens of bristles into a single hole. The holecan be of many shapes but what is common to all is a low aspect ratiowith a circular hole having an aspect ratio of 1.0 and oval orrectangular holes having aspect ratios of up to 10. When packed intothese holes, most bristles are in contact with and thus have frictionwith neighboring bristles on many or all sides. This increases bristlestiffness of a given diameter bristle through the support provided bythese neighboring bristles and effectively shortens the length which isfree to move. By comparison, a bristle sub-assembly according to thosedescribed herein have relatively large aspect ratios. Therefore, anindividual bristle has fewer neighboring bristles to interact with andbe supported by, and thus, is less stiff.

[0038] Referring to FIG. 7, modeling of Nylon brush filaments wasperformed and the results are presented. A Nylon bristle diameter of0.006 inch was used as a constant, while the base string was varied,using steel as the base for comparison to a torsionally “stiff”material. On the horizontal axis, the distance along the base filamentis shown in inches. Attachment is assumed over a one inch span, withpeak deflections shown at the mid-point between the span. The steel basestring is shown to have no deflection, due to its inherent propertiesand the force applied. However, the degree of deflection increases withthinner diameter, lower modulus, polymeric base strings. In conclusion,it can be seen that bristle deflection varies from end bristle to centerbristle, and that the base filaments deflect only slightly. Moreover,deflection is the sum of bristle cantilever bending plus base filamentrotation, and base filament diameter has a large influence on bristledeflection.

[0039] The use of a spanning bristle sub-assembly, or for connecting abristle sub-assembly at different points while leaving portionsunconnected, has numerous possible uses in different brush types. Forexample, in a vacuum attachment, an open brush head attachment wouldallow the air to flow up through the bristle structure and keep air flowresistance to a minimum since the bristles do not need to becontinuously embedded in a support structure. In this case, hightorsional stiffness may be preferred for general cleaning so there islittle torsional deflection across the length of bristles.

[0040] In some abrasive brush applications, the use of the side of thebristle is preferred over the tip of the bristle. When relatively largebristles are used they do not bend easily and therefore are limited moreto the tip. By attaching them to a supporting base structure whichtorsionally twists under load, the bristles would then tend to lay awayfrom the direction of rotation and expose more of the bristles side,thus increasing the contact area between the work and the bristles(thereby gaining efficiency).

[0041] In cleaning brushes, brushes used in applications such as on theend of a garden hose for car washing should be soft while allowing thefluid (cleaning solution or rinse) to work together with the bristles. Apreferred attachment would allow the solution to be discharged at thebase of the bristles. This serves to not only continuously wet thebristles but to cleanse the bristles from entrapping harmful dirtparticles. Soft bristles are required to prevent damage to the carfinish. The sides of a bristle will do less abrasion to the finish thanthe pointed ends of a bristle. Therefore more rigid (aggressive)bristles could be used if they torsionally deflect to expose the bristleside rather than the tip.

[0042] In other brush designs, a bristle sub-assembly which has asufficiently stiff base structure may not need a supporting head or wireas is typically understood in the art. The base structure of thesub-assembly could be directly attached to a handle such as in a mascarabrush or bottle brush. With the proper cross-section of the basestructure to which the bristles are attached, the base may be relativelystiff to bending, yet torsionally soft. This would allow the bristles tobe stiff using an axial movement and soft using a rotational movement.

[0043] In general, the bristle sub-assemblies need not be connected atthe ends of the base string, as would be the case where a bristlesub-assembly is suspended across an opening in a brush head or othersupporting structure. For example, in FIG. 8, a bristle sub-assembly 64includes a base string 66 and a row of bristles 68. In this case, thebristle sub-assembly is connected to an upper surface of a brush head 70at spaced intervals, such as by spot welds 72, 74 and 76. Consistentwith the teachings above, the bristles nearest the spot welds will havethe greatest apparent stiffness, due to the spot welds' limiting effecton the amount of torsional movement of the base string 66. However, theamount of limitation provided by the spot welds can be controlled bycontrolling the amount of surface area of the base string that iscovered by weld material. A complete covering of the base string withweld material will have a maximum limiting effect.

[0044] The spot welds can be formed by any conventional means, includingultrasonic heating (assuming one or both of the bristles and base stringare made of polymeric material), adhesive bonding, conventional heating(coupled with plastic deformation), and virtually any other suitablemeans. Also, if the base string 66 is connected continuously along thesurface of the brush body, along a weld line, or glue line, if theconnection is only at the tangent point between the base string 66 andthe surface, the bristles will appear less stiff due to the torsionalmovement of the base string which is permitted by the fact that the basestring is not completely bound throughout its circumference. Thus,controlling the circumferential degree of binding of the base string tothe underlying brush structure will result in controlled stiffness.

[0045] For some applications, very fine filaments are preferred fortheir softness and their ability to penetrate small areas, such as, inthe case of a toothbrush, small interdental and gingival areas. Theirsmall cross-section, however, makes them weak and less durable when usedin a toothbrush. Thus, another aspect of the present invention is toprovide an elastomeric coating to a bristle sub-assembly whichreinforces the filaments of the bristle sub-assembly from the bondedarea up to a predetermined height. The height is selected to yield thedesired stiffness of the tuft. This structure would resemble that of aused paint brush improperly cleaned, where the base portions of thebristles becomes thicker than the distal end portions, due to drying andhardening of paint on the base portions.

[0046] The coating of bristles permits fine filaments such as 25 milfilaments to be used entirely within a tuft and have the apparentstiffness of larger diameter filaments such as 6-10 mil. FIG. 6illustrates such a coated bristle sub-assembly 52, in which the two rowsof bristles 54 and 56, connected at their proximal ends to a base string58, are provided with polymeric coatings 60 and 62 along the proximalend portions of the bristles. The length to which the coatings extend,as well as their thicknesses are material properties, such as hardness,will determine the amount of stiffness added to the fine bristles.

[0047] The coatings can be elastomeric resins or other suitablematerials. They could further provide functionality with respect to awear indication, bactericide or other desired properties difficult toincorporate into the monofilament bristle itself. The elastomeric resincoating can reduce the possibility of bristle shedding from the bristlesub-assembly, by adding additional adhesion between the base string andthe bristles. It could also be used by the brush maker as a bondingagent in the process of making brushes, particularly where techniquesthat do not employ base strings are employed.

[0048] The non-bonded end of the bristle sub-assemblies would not becoated, nor attached to the adjacent filaments. Such a structure wouldhave similar performance to a tapered filament. This structure wouldalso tend to resist splaying. The stiffness of a given filament would bedetermined by the relative viscosity of the resin used, the thickness towhich it is applied, and the area (height) to which the bristle istreated. Coatings would have particular applicability to toothbrushes,which are limited to a minimum of 5 mil bristles. These small diameterbrushes have relatively shortened periods of useful life, due to wearthat leads to splaying. In conventional tufted brushes, it woulddifficult if not impossible to apply thin coatings to the bristles, dueto the packing of bristles in a dense tuft hole, nor can select bristlesbe coated for the same reason. Using the bristle sub-assembliesdescribed herein as well as in the copending applications, the brushmaker can apply thin coatings onto pre-selected portions of thebristle/tuft.

[0049] To form the coatings on the bristles, the individual strandscould be individually coated or stuck together for some given length,leaving the remaining length free, by solution coating, or by hot meltcoating with a polymer having a lower melt point. The solution coatingcould be, as described in the Nylon Plastics Handbook by M. I. Kohan, pp286,287, Dupont's Elvamide® terpolymers such as a 6/66/610 or 6/66/69.Terpolymers are soluble in hot methanol or methanol/water solutions.These are typically used for thread bonding.

[0050] The hot melt coatings could be Low melting nylon such as thosemade for hot melt coating. An example is Platamide H105, a 6/66/12 nylonterpolymer by Elf Atochem or Griltex®1 from EMS. Additional examplesinclude Pebax® nylon elastomer by Elf Atochem to thermally bond to nylonfilament, and Hytrel® polyester elastomer to thermally bond to polyesterfilament. Further examples include low melting materials grafted withreactive material such as maleic anhydride. An example is Kraton®FG1901X, a SEBS block copolymer modified with maleic anhydride. Anexample of glues that could be used herein are cyanoacrylate, soldcommercially as “Super Glue.”

[0051]FIGS. 9 and 10 illustrate a bristle sub-assembly 78 which, as inthe previously described sub-assemblies, includes a base string 80 andtwo rows 82 and 84 of bristles. The scale shown in FIGS. 9 and 10 isexaggerated to highlight features at the proximal ends and distal endsof the bristles. Also, the base string is shown to be rectangularlyshaped and disposed between the rows of bristles, although virtually anyshape can be employed. Also, the base string can be any device that actsas a support beam for suspending the bristle sub-assembly acrossopenings, or simply for supporting the beam at select positions to allowthe beam to undergo torsional movement during brushing action of thebristles.

[0052] As seen in FIGS. 9 and 10, the distal end portions of thebristles are sheared and have substantially the same thickness as theproximal ends that are connected to the base string 80. According to thepresent invention, the stiffness of the bristles can be changed bymechanically abrading the distal end portions to provide a taper, asshown in FIGS. 11 and 12. The abrading process provides a taperedportion 86 for the bristles that can go down the length of the bristlesapproximately 33% of the overall length.

[0053] Tapering changes the apparent stiffness of the bristles. Forexample, a 10 mil filament can be worked with an abrasive belt toundergo a reduction down to 10% of its original diameter, for example,to result in a 1 mil thickness at the tip. The taper can begin as fardown the bristle as 33% of the overall length. Beyond that, the limitsare efficiency, in that it may be more efficient to begin with a thinnerbristle than to taper more than 33% of the overall length.

[0054] While an abrasive belt is one method of abrading and thus formingthe taper on the bristle distal end portions, other means can beemployed.

[0055] The present invention has been described above with reference topreferred embodiments. However, those skilled in the art will recognizethat changes and modifications can be made in these preferredembodiments without departing from the scope of the present invention.Accordingly, these and other changes and modifications which are obviousto those skilled in the art are intended to be included within the scopeof the present invention.

What is claimed is:
 1. A bristle sub-assembly comprising: at least onerow of bristles, the bristles having proximal ends and distal ends; anda coating disposed on at least the proximal end portions of thebristles, the coating having mechanical properties selected to stiffenthe distal ends of the bristles.
 2. A bristle sub-assembly according toclaim 1, wherein the coating is made of an elastomeric resin.
 3. Abristle sub-assembly according to claim 1, wherein the proximal ends ofthe bristles are connected to a support beam.
 4. A bristle sub-assemblyaccording to claim 1, wherein the coating covers at least a portion ofthe proximal end portions of the bristles.
 5. A bristle sub-assemblyaccording to claim 1, wherein the support beam is selected from thegroup consisting of a glue line, a base string, and a bond areaconsisting of melted bristle material.
 6. A bristle sub-assemblyaccording to claim 1, wherein the coating is made of a material selectedto provide additional functionally selected from the group consisting ofwear indication and therapeutic properties such as a batericide.